package cn.tac.framework.easydev.core.util;

import com.google.common.collect.Lists;
import org.apache.commons.lang3.StringUtils;

import java.util.ArrayList;
import java.util.List;
import java.util.UUID;

/**
 * ID生成器,用于生成ID
 *
 * @author tac
 * @since 2.0
 */
public abstract class IDUtils {
    public static final boolean COMPACT_UUID_DEFAULT = true;
    private static String compactEmptyUUID;
    private static String nonCompactEmptyUUID;

    public static String UUID() {
        return UUID(COMPACT_UUID_DEFAULT);
    }

    public static String UUID(boolean compact) {
        if (compact) {
            return UUID.randomUUID().toString().replace("-", "");
        } else {
            return UUID.randomUUID().toString();
        }
    }

    public static String emptyUUID() {
        return emptyUUID(COMPACT_UUID_DEFAULT);
    }

    public static String emptyUUID(boolean compact) {
        if (compact) {
            if (StringUtils.isBlank(compactEmptyUUID)) {
                compactEmptyUUID = buildEmptyUUID(compact);
            }
            return compactEmptyUUID;
        } else {
            if (StringUtils.isBlank(nonCompactEmptyUUID)) {
                nonCompactEmptyUUID = buildEmptyUUID(compact);
            }
            return nonCompactEmptyUUID;
        }
    }

    public static SnowFlake snowflake(long datacenterId, long machineId){
        return new SnowFlake(datacenterId, machineId);
    }

    private static String buildEmptyUUID(boolean compact) {
        List<Integer> ls = Lists.newArrayList(8, 4, 4, 4, 12);
        StringBuilder sb = new StringBuilder();

        for (int i : ls) {
            for (int j : range(i)) {
                sb.append(0);
            }
            if (!compact) {
                sb.append("-");
            }
        }
        String id = sb.toString();
        if (!compact) {
            id = id.substring(0, id.length() - 1);
        }
        return id;
    }

    private static List<Integer> range(int count) {
        List<Integer> ls = new ArrayList<>();
        for (int i = 0; i < count; i++) {
            ls.add(i);
        }
        return ls;
    }


    /**
     * twitter的snowflake算法 -- java实现
     * <a href="https://github.com/beyondfengyu/SnowFlake/blob/master/SnowFlake.java">beyondfengyu/SnowFlake</a>
     *
     * @author beyond
     * @since 2016/11/26
     */
    public static class SnowFlake {

        /**
         * 起始的时间戳
         */
        private final static long START_STMP = 1480166465631L;

        /**
         * 每一部分占用的位数
         */
        private final static long SEQUENCE_BIT = 12; //序列号占用的位数
        private final static long MACHINE_BIT = 5;   //机器标识占用的位数
        private final static long DATACENTER_BIT = 5;//数据中心占用的位数

        /**
         * 每一部分的最大值
         */
        private final static long MAX_DATACENTER_NUM = -1L ^ (-1L << DATACENTER_BIT);
        private final static long MAX_MACHINE_NUM = -1L ^ (-1L << MACHINE_BIT);
        private final static long MAX_SEQUENCE = -1L ^ (-1L << SEQUENCE_BIT);

        /**
         * 每一部分向左的位移
         */
        private final static long MACHINE_LEFT = SEQUENCE_BIT;
        private final static long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
        private final static long TIMESTMP_LEFT = DATACENTER_LEFT + DATACENTER_BIT;

        private long datacenterId;  //数据中心
        private long machineId;     //机器标识
        private long sequence = 0L; //序列号
        private long lastStmp = -1L;//上一次时间戳

        public SnowFlake(long datacenterId, long machineId) {
            if (datacenterId > MAX_DATACENTER_NUM || datacenterId < 0) {
                throw new IllegalArgumentException("datacenterId can't be greater than MAX_DATACENTER_NUM or less than 0");
            }
            if (machineId > MAX_MACHINE_NUM || machineId < 0) {
                throw new IllegalArgumentException("machineId can't be greater than MAX_MACHINE_NUM or less than 0");
            }
            this.datacenterId = datacenterId;
            this.machineId = machineId;
        }

        /**
         * 产生下一个ID
         *
         * @return
         */
        public synchronized long nextId() {
            long currStmp = getNewstmp();
            if (currStmp < lastStmp) {
                throw new RuntimeException("Clock moved backwards.  Refusing to generate id");
            }

            if (currStmp == lastStmp) {
                //相同毫秒内，序列号自增
                sequence = (sequence + 1) & MAX_SEQUENCE;
                //同一毫秒的序列数已经达到最大
                if (sequence == 0L) {
                    currStmp = getNextMill();
                }
            } else {
                //不同毫秒内，序列号置为0
                sequence = 0L;
            }

            lastStmp = currStmp;

            return (currStmp - START_STMP) << TIMESTMP_LEFT //时间戳部分
                    | datacenterId << DATACENTER_LEFT       //数据中心部分
                    | machineId << MACHINE_LEFT             //机器标识部分
                    | sequence;                             //序列号部分
        }

        private long getNextMill() {
            long mill = getNewstmp();
            while (mill <= lastStmp) {
                mill = getNewstmp();
            }
            return mill;
        }

        private long getNewstmp() {
            return System.currentTimeMillis();
        }

        public static void main(String[] args) {
            SnowFlake snowFlake = new SnowFlake(2, 3);

            for (int i = 0; i < (1 << 12); i++) {
                System.out.println(snowFlake.nextId());
            }

        }
    }
}
